1. Field of Invention
The claimed inventions herein relate to transparent thermoplastic polymer blend compositions for use in molded and extruded articles.
2. Description of Related Art
A variety of transparent thermoplastic compositions have been developed, some of which have been disclosed in the patent literature and/or introduced to the marketplace. Each of those compositions has a particular level of transparency, often characterized in terms of “haze,” which is expressed as a percentage (%) in accordance with recognized test procedures. Shortcomings of those compositions include unsatisfactorily high haze values (low transparency), poor processability and poor mechanical properties, including undue hardness, low flexibility, etc. For example, previously proposed thermoplastic elastomer compositions with transparency and flexibility such as compounds based on styrene-ethylene-butadiene-styrene block copolymers, thermoplastic vulcanizate blends (TPV) or thermoplastic olefin (TPO) blends have reached transparency and softness levels that are still unsatisfactory in some applications.
It is among the objects of the invention to provide a transparent material that has a desirable balance of softness, flexibility and strength, and which can be easily processed in a molten state in extrusion or molding.
Polymer blends prepared for various applications are known. Adhesive blends that include hydrocarbon resins are disclosed in PCT Application No. WO 2004/087806. In Example 4 certain compositions include hydrocarbon resin with Tg>20° C. blended with two different types of polypropylenes, namely, minor amounts of polypropylene having a Tm≧110° C. and major amounts (72 wt % and above) of propylene-ethylene copolymer that has isotactically arranged propylene derived sequences and Tm<105° C.
U.S. Pat. No. 5,317,070 also discloses adhesive compositions that include a hydrocarbon resin with high glass transition temperature, but the polymers with which the compositions are blended are different from the polypropylenes claimed herein.
U.S. Pat. No. 6,500,563 discloses blends of two different types of polypropylene, including blends made from a polypropylene having a Tm≧110° C. and propylene-ethylene copolymer that has isotactically arranged propylene derived sequences and Tm<105° C.
Three component blends of isotactic polypropylene, impact modifying amounts of an ethylene propylene based rubber or low density ethylene copolymer and a propylene based elastomer as compatibilizer are described in EP946640, EP946641 (WO 98/027155), EP969043 and EP1098934.
WO04/014988 describes blends of isotactic polypropylene with non-functionalized plasticizers such as poly-alpha-olefins.
Unpublished U.S. Application Ser. No. 60/434097 filed 17 Dec. 2002 describes blends of polypropylene and propylene based elastomers to provide flexibility.
Dow WO03/040233 also discloses two component blends with the isotactic polypropylene as the predominant, matrix phase and the propylene-based copolymer serving as an impact modifier.
EP1003814 and U.S. Pat. No. 6,642,316 disclose two-component blends of small amounts of isotactic polypropylene and predominant amounts of an ethylene based elastomer.
EP374695 (WO 98/027155) Example 5 discloses visually homogeneous two component blends however using 40 wt % or less of the propylene-based copolymer.
WO00/69963 describes films made of two-component blends with from 75 to 98 wt % of a propylene ethylene based elastomer having a heat of fusion of less than 25 J/g. A process oil may be present.